Conventional pressure sensors in which plural electrical conductors are arranged apart from each other are known (see, e.g., PTLs 1 and 2). Such pressure sensors become in an electrically conducted state by contact between the plural electrical conductors when receiving an external force, thereby functioning as a switch.
The pressure sensor described in PTL 1 has a structure in which four linear electrode wires are spirally arranged with spaces therebetween so as not to be in contact with each other along an inner peripheral surface of a cylindrical insulation, and is thereby capable of reliably detecting an external force in all directions. These electrode wires are each composed of an electrical conductor formed by twisting tin-plated soft copper wires, and a conductive rubber covering the surface thereof. It is disclosed that the conductive rubber contains carbon black.
A cord switch described in PTL 2 is a linear pressure sensor and has a structure in which an end portion of a rubber cover covering the outer periphery of a cylindrical insulation is sealed with a hot-melt resin. Curing time of a sealant is reduced since the hot-melt resin is used as the sealant, and it is thus possible to efficiently manufacture the cord switch. The plural electrical conductors provided in this cord switch are each composed of a core wire and a conductive resin covering the surface thereof. The details of the conductive resin are not disclosed.
Meanwhile, a highly processable conductive rubber composition used as a material for electrical conductor of pressure sensor is known (see, e.g., PTL 3). The conductive rubber composition described in PTL 3 is obtained by adding an ethylene-α-olefin copolymer and carbon as a conductivity imparting agent to a base rubber having a Mooney viscosity ML1+4 (100° C.) of not more than 40.